Like all other components, capacitors used in microelectronics must be further and further miniaturized in order to make correspondingly smaller, more energy-saving or merely more powerful terminal devices possible. For capacitors, dielectrics with relatively high dielectric constants can be used. Dielectric constants of more than 1000 can be achieved with ferroelectrics such as lead zirconate titanate (PZT), barium strontium titanate (BST), strontium titanate and others, depending on material and composition. When a voltage is applied to such ferroelectrics, piezoelectric behavior often appears in these materials, wherein the piezoelectric constant of these materials rises above 0.1 C/m2. In addition, the relative dielectric constant is usually likewise voltage-dependent. This opens the possibility of producing capacitors with ferroelectrics that are voltage-dependent or tunable by varying voltage.
Miniaturized capacitors and capacitors produced with thin-film technology can be structured as a plate, an interdigital, or a trench arrangement (pit capacitors). The highest capacitance densities, i.e. the highest capacitance of the thin-film capacitor per unit surface of the substrate material, are achieved with pit capacitors. These are difficult to manufacture, however. Plate capacitors with a dielectric layer arranged parallel to the substrate surface between two electrodes can achieve a capacitance density of up to 100 fF/μm2 with the ferroelectric at a dielectric thickness of roughly 100 nm. A capacitor with a 10 pF capacitance then has a surface area of only 10×10 μm2.
Components constructed as plate capacitors in multilayer technology can achieve further increased capacitance densities, but are technologically more complicated. Interdigital capacitors, for which only one metal layer need be structured as an interdigital structure, are easy to manufacture. With a typical electrode spacing of roughly 500 nm, the capacitance densities that can be achieved are less than 1 fF/μm2. A capacitor with a 10 pF capacitance then has a surface area of more than 10×100 μm2.